Not applicable.
Not applicable.
The present invention relates to the field of postal automation and handling and in particular to the detection of overlapping mail pieces conveyed during the postal handling process. The mail pieces at issue are, generally, flat and flexible, and transported in a sequence by a conveyor belt and the like.
Sorting devices incur problems when sorting mail pieces, namely, dual subtraction errors or the unintended removal of an overlapping mail piece along with the intended removal of the mail piece being overlapped. The intended mail piece is usually the leading mail piece. Numerous reasons exist for overlapping mail pieces and dual subtraction, including friction between the two mail pieces and over-protruding leading mail pieces. By this error, the overlapping mail pieces are unintendedly sorted to usually wrong locations within the mail handling system. In addition, the error distribution rate increases and an increase probability of mechanical interference and/or failure caused by the overlapping mail piece may result. One result to the above problem is to identify overlapping mail pieces and treat them as rejected mail items. Accordingly, the aforementioned results of this problem may be avoided.
One proposed solution includes the identification of overlapping mail pieces. One form of identification includes applying a pattern, such as a bar code, to the length of the mail piece and/or scannable traces on the front and back side of the mail piece. The pattern is then scanned for interruptions, the interruptions indicating a blockage of the scan and therefore an overlap. This solution requires the initial steps of applying the pattern or trace onto the mail piece. In a second step, the mail items are set aside for more precise distribution and then overlaps may be identified. By this solution it is not possible to detect overlaps in a first mail run through a distribution plant given that this occurs prior to the application of the pattern or trace. The high mechanical expenditure which has to be driven to flex-level or to bend the mail items in order to detect possible pattern or trace interruptions is also a disadvantage of this solution. Another disadvantage is that the pattern or trace may only be applied onto portions of mail items which are not covered up by shipping straps.
Another solution is proposed in EP 028 056 which sets out an apparatus wherein edges of mail items are detected by light sensors and diagonal illumination. With the help of a control switch it is then determined if a dual subtraction exists. This method has a high error rate due to the varying condition of the surface of the mail items arising for example from dirt accumulations.
A still further solution is proposed in U.S. Pat. No. 3,578,315 which also makes use of light sensors to detect dual subtractions. It is thereby assumed that diffused light, based on an illuminated letter, is brighter than diffused light during a dual subtraction. This method has a very high error rate because the letters normally have varying degrees of transparency.
Yet another solution is proposed in EP 0 650 911 B1 wherein at least one deflection element is placed within the hauling path, by which movable portions of the mail items are deflected temporarily vertically to the hauling direction. The presence of overlapping portions of mail items is then detected by a detection facility based on the spring-return mechanism of the rearward deflected (in hauling direction) portions of mail pieces. This solution is mostly independent from the condition of the surface of the mail pieces.
An advantage of the present invention is to overcome the problems of the above set out solutions. Another advantage is to provide a system which may easily be integrated into existing mail sorting systems at reasonable costs and easy manufacturability. These and other advantages are provided by the present system and method for detecting overlapping mail pieces.
The present invention comprises a system for detecting overlapping in-coming mail pieces carried along a track, comprising: a deflecting element for deflecting said mail pieces, said deflecting element positioned within said track so as to engage said mail pieces, at least one light barrier comprising a beam source and a detector element, said beam source emitting a light beam directed at a detector element, said at least one light barrier positioned proximate to said deflecting element such that an in-coming mail piece deflected by said deflecting means interrupts said light beam, and determination means for determining if said light beam has been interrupted more than once within a time T defined by the relationship Txe2x89xa6L/F, wherein L is the approximate length of a deflected mail piece and F is the in-coming speed of the in-coming mail pieces.
The present invention further comprises a method for identifying an occurrence of an overlapping in-coming mail piece being conveyed along a track, comprising the steps of: determining a length of said mail piece; determining an in-coming speed of said mail piece; deflecting said mail piece; and determining if a first light barrier is broken during a time T defined by the relationship Txe2x89xa6L/F, wherein L is the approximate length of a deflected mail piece and F is the in-coming speed of the in-coming mail pieces.
Because mail items comprises varying lengths, it is insufficient to detect the overlaps only in the rear portions of mail items (with respect to the conveyance direction) by detection of short successively rotating rear edges. Overlaps may also occur when the rear edges of the stacked mail items are essentially superimposed and only the front edges are a bit offset. In such circumstances, the solution set out in EP 0 650 911 B1 becomes inoperative. For overcoming at least this deficiency, the present solution, as set out in the claims, deflects movable front portions of mail items away from the conveyance direction.
The present system may be placed on either or both sides of the conveyance path in so as to detect leading edges with respect to trailing edges and overlaps from either side.
In another embodiment, the present apparatus may comprise a rotating smooth disk for deflecting mail pieces. The disk may be positioned at an angle or diagonally to the on-coming mail pieces. Rotating speed of the disk may be selected to approximately match the conveyance rate.
In a further embodiment the disk includes a plurality of teeth separated by gaps, the teeth being arranged about the circumference of the disk and rotating at such a speed and direction that the teeth engage a leading edge of an in-coming mail piece and the gaps engage any subsequent overlapping mail pieces. An advantage to this embodiment includes avoiding deformations of the mail pieces.
In a still further embodiment, another rotating disk may be added so as to take the tension off of the deflected portions of the mail pieces.